Some oil and gas reservoirs in Nigeria are often weakly consolidated, making them liable to sand production. During upstream petroleum production operations, light oil and sand mix from the reservoirs are produced through wells dug into formation zones and transported through horizontal pipes between well heads and flow stations. The residual sand transported through the pipes pose serious problems such as, blockage and, reduction of pipe efficiency and integrity. A mathematical simulation of the transport process of crude oil and sand in a horizontal pipe is discussed in this book. The model used is a modified form of the Doan et al (1996 and 2000) models. The effect of eddies in three regions was incorporated in the mass and momentum equations of the model and a third equation for solid phase was also developed. Difference formulae were generated for the conservation equations by applying Fick's equation for diffusion as a basis for the origin of the finite difference formula. The diffusion equation was modified and applied to the momentum phase equations so as to make the model have a clear solution. The method adopted in this book, rather than the usual method of solving models